


A Billion Familiar Beats of Your Heart

by leveragehunters (Monkeygreen)



Series: A Game of Cat and Mouse [2]
Category: Captain America (Movies)
Genre: Alternate Universe - Animals, Alternate Universe - Modern with Magic, Alternate Universe - Modern: No Powers, Bucky is a cat, Cats, Familiar Bucky Barnes, Fluff, Fluff and Angst, M/M, Magical Realism, Mice, Ridiculous, Skinny Steve, Steve is a mouse, Witch Natasha Romanov, animal to human transformation, happy birthday steve rogers, if I stumbled into your area of expertise mea culpa, reliance on popular science
Language: English
Status: Completed
Published: 2018-07-04
Updated: 2018-07-04
Packaged: 2019-05-30 19:31:04
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 6,323
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/15103433
Author URL: https://archiveofourown.org/users/Monkeygreen/pseuds/leveragehunters
Summary: Cats didn't need to wonder how long mice lived, because they knew: mice lived exactly as long as it took a cat to pounce andbite.But Bucky wasn't just a cat. He wasSteve'scat, Steve washismouse, and maybe it was his imagination, but he thought Steve might be starting to slow down.





	A Billion Familiar Beats of Your Heart

**Author's Note:**

  * For [koreanrage](https://archiveofourown.org/users/koreanrage/gifts), [cyborgtopus (allrealities)](https://archiveofourown.org/users/allrealities/gifts).



> This is dedicated to [lenadraws](http://lenadraws.tumblr.com/)/[ellebeesknees](http://ellebeesknees.tumblr.com/) and [koreanrage](http://koreanrage.tumblr.com/) for drawing such wonderful art for _Probably Not What They Meant by a Game of Cat and Mouse_ —thanks again so much, guys. I adore both pieces beyond words. It's also for [cyborgtopus](http://cyborgtopus.tumblr.com), who posted a kitty and a rattie the other day, mentioned A Game of Cat and Mouse in the tags, and made me smile on a day I really needed it. 
> 
> Written to celebrate Steve Rogers hundredth birthday (even if Steve doesn't actually get a birthday in it!).
> 
> ETA: Minor edits made 6 July to correct a wee continuity (catinuity?) error. Carry on!  
> ETA2: Oh my GOSH look what koreanrage drew!! [Bucky and Steve sleeping](http://koreanrage.tumblr.com/post/175668945815/i-swear-im-working-on-remaining-prompts-but-i-had). Please go give her all the love and rebologs on Tumblr!

Head low, Bucky lifted his right rear paw and froze, awkwardly balanced on the diagonal. The tall grass waved around him, obedient to the demands of the breeze, but Bucky stood stock still, unmoving.

Despite his insistence on ignoring its demands, the breeze still deigned to bring him a scent. His whiskers quivered, seeking, searching.  _There._

All three paws once more lightly planted, he slid through the grass like a furred snake, not hampered in the slightest by his missing front leg. A flower garden bordered the grass, thick green stalks rising from the groundcover that hid the dirt. _Disturbed_  groundcover, and the scent was strongest there.

Pupils narrowing, he prepared to pounce, wriggling his butt (for even cats must sometimes sacrifice dignity in pursuit of greater ends), the tip of his tail twitching as he held, waiting for the perfect moment.

Waiting.

Waiting.

Waiting…  _NOW!_  Bucky was an explosion in motion, the perfect expression of  _cat_ , leaping forward, front paw slapping down on the groundcover, claws carefully retracted.

"Gotcha!" he yowled triumphantly to…

Nothing.

The disturbed spot was empty, chewed up leaves and dug up dirt that reeked of Steve mocking him with their complete lack of Steve.

Bucky sat back, ears flat, grumbling, trying to ignore the nibbling edge of worry at the absence of his mouse since it was, after all, the point. 

The green area at the back of the building that no one ever mowed was perfect for what Natasha _insisted_  on calling hide and seek. Which it wasn't. Hide and seek was a game for human children. He and Steve weren't playing a _game._ They were keeping their skills sharp. Honed. Bucky ruled these streets, this garden, no one would dare so much as glance at Steve in Bucky's presence, but he needed to know Steve would always be safe, even if he _wasn't_ there. He needed to know Steve could keep himself safe from all the cats who weren't Bucky. The ones who'd look at him and see only a small grey mouse, who'd see  _prey_  (Bucky fought down the urge to fluff out his fur and scream a challenge) and not the wonderful amazingness loaded into that tiny package.

Steve wasn't prey. Steve would never be prey. That Steve had just lured Bucky into thinking he'd catch him so easily only proved it.

A quiet noise jerked Bucky's head up just in time to see a tiny, pale pink nose poke out from between two fat tulip leaves. Before he could say anything, Steve thrust his head the rest of the way through, eyes half-lidded, ears curved forward, radiating pleased smugness.

"Looking for something?"

Bucky turned his head and began pointedly grooming his shoulder.

Steve laughed at him. "You think you'd learn to look up by now."

Bucky groomed his shoulder  _even more pointedly_ , making sure not a hair was out of place.

"It's not higher than the fridge," Steve pointed out.

Bucky still didn't look at him, because the fur on that shoulder was very messy and, what with him having no leg on that side, it was important that it look its best.

Steve laughed again and swarmed out of the tulip, tail curled around the thick stem for balance as he scurried down to the ground, and sat on Bucky's front paw.

Bucky glanced down at him and flicked his ears forward. Steve's grey fur was dusted with light yellow. "You're  _covered_  in pollen," he said, and rasped his tongue over Steve's back.

Then sneezed. Twice.

Steve hunkered down, gazing up at him in amusement, ears canted back and tail curled around Bucky's paw. "Sorry,  _who's_  covered in pollen?"

Bucky stuck out his tongue and worked his jaw. "You taste like honey. Or something. Something weird. You don't taste like you. "

"You're the one who decided to lick me."

"I'm a cat! It's what I do!"

Steve stretched up on his back legs to rub his cheek against Bucky's chin, entirely unmouse-like behaviour he'd picked up from Bucky, and Bucky started to purr.

"Let's go home?" He pressed the tip of his nose against Bucky's and hummed, low and sweet. "You can lick me some more."

Steve's tattoo, the swooping lines of the rune Natasha had given him, were barely visible through his pale grey fur, but it was there. Just like Bucky's. And just like Bucky's, it let Steve swap his body for a human one. They were a cat and a mouse, those were the bodies they belonged in, but being human offered so many more ways to be together. So many  _excellent_  ways of being together. Ways of being together Bucky deeply enjoyed. Not just the sex (although don't get him wrong, the sex was  _great_ ; humans had it  _way_  too good when it came to sex); it was the touching and the kissing, the holding and the being held. All the things they couldn't do shaped like this.

Suddenly he was in a hurry to get them upstairs.

"Climb on." He crouched low and Steve climbed up his leg, settling between his shoulder blades. There was irony there, Bucky thought: Steve was a tiny grey shadow no one would notice, but his weight felt like the world to Bucky.

Which just made sense, he guessed, even if it was something he'd never share with anyone—he was a cat; there were  _standards_ —because Steve  _was_  his world. Natasha was his witch and Steve was his world and he'd never in his life known he could be this happy.

A few nights later, Bucky yawned and stretched, uncurling from sleep as the sun began to set. He could hear Natasha moving around, knew she was getting ready to go out to meet Clint. They were planning something, he had no idea what, and since it didn't involve him or Steve, he wasn't all that interested. She'd tell him if she needed him to know, or he'd find out on his own if it piqued his interest.

He absently licked his paw, rubbed it against his face, and blinked lazily at the world. Something was different, but he couldn't quite…

Oh. Steve was still asleep.

There were two places Steve slept when he was a mouse: an indentation like a paw print at the side of Bucky's bed, perfectly sized for his tiny body, or snuggled into Bucky's fur—against his belly, against his chest, in the space where Bucky's leg used to be—always curled in a tidy circle, his long tail draped over his nose.

Right now, he was sleeping in the little hollow. Bucky watched him, watched the rapid rise and fall of his ribs, the way his whiskers twitched, and laid his ears back. The sun was setting. Steve was always up and running around at sunrise and sunset, usually while Bucky was trying to nap—half the time Steve woke  _Bucky_ , tugging on his whiskers or running clever paws through his fur while he whispered in Bucky's ear—but here he was, still sleeping.

He gently nosed him, ruffling his short fur. Even in sleep, Steve uncurled, exposing his belly, and lifted a paw to pat at Bucky's nose. Warmth rushed through him and a purr rumbled to life all on its own.

Steve woke at the sound, yawning and stretching, black eyes cloudy with sleep. "Bucky." It was soft and happy and Bucky put his head down, nose against Steve's belly, and breathed in, the scent of Steve wreathing through him. Steve grabbed hold of his whiskers and tugged gently and all was right with Bucky's world, his momentary concern forgotten.

There were certain realities about life with a mouse, one of which was the sound of the wheels.

Natasha kept them oiled, so they didn't squeak, but the constant whirr and rattle as Steve ran would fill the apartment. It was ubiquitous background noise, like the hum of traffic through the window, not something Bucky even noticed.

No, what he noticed was when the noise changed. When it slowed down.

Bucky propped his chin on the edge of Steve's habitat. "You feeling all right, Steve?"

Steve's legs were still a blur, even if they weren't going as fast as Bucky was used to, and Steve looked at him in confusion as the plastic wheel gradually slowed to a stop, rocking gently back and forth. "Yeah? I feel fine. Why?"

Steve's eyes were the same bright bold black they'd always been, his fur thick and soft. Bucky wondered if he was imagining things. "Nothing, Steve. No reason. Go back to running." He tilted his ears to the side. "You know its never going to get you anywhere, right?"

With a flick of his tail, Steve pointedly hopped off his wheel and climbed onto one further away—one that let him turn his back on Bucky. Bucky grinned a cat grin and didn't say anything, just kept watching Steve, the comforting sound of the rattling wheel filling the apartment.

But he didn't think it was his imagination that it was slower.

Bucky, fast asleep on the windowsill overlooking the fire escape, felt gentle fingers rubbing behind his ear. He didn't open his eyes, but he flicked an ear and started to purr.

Natasha switched to the other ear, knowing just the spots to hit, and Bucky's purr intensified as he felt Steve climb through his fur to the top of his head to greet her.

"Steve," she said, and Bucky knew she'd be offering her other hand, knew Steve would be delicately nibbling her fingernails, one paw on her hand for balance.

He loved Steve, but mice were weird. Thankfully, Natasha seemed to understand that nibbling was both high regard and high compliment from Steve. "You're weird," he muttered when Steve slid down his shoulder to once more curl up under his chest.

"I'm  _polite_ ," Steve corrected. "She's your witch and you can't even be bothered to open your eyes."

Bucky did so and sat up, both in an extremely dignified manner, not deigning to answer, although a quick glance showed Steve looking deeply amused, ears curved forward, tail curled neatly around his paws. Bucky nosed Natasha's hand and rubbed his face against her palm.

"I need you...if you can spare the time," she said, with definite overtones of sarcasm. Bucky was proud of her. That was almost cat-worthy. "Both of you," she added, sarcasm gone, gently touching the end of Steve's tail to get his attention. "If Steve doesn't mind."

"Time to do my job," Bucky said. "And she'd like you to help."

"Got that, yeah," Steve said, standing on his back legs to sniff in Natasha's direction. She offered her hand again and he put both front paws on her finger. It was his way of saying yes.

Natasha smiled. "Thank you."

Bucky sniffed. "What about me?"

She couldn’t understand him, not when he was like this, but she must have got the gist, because she grinned wryly. "And you, of course, Bucky," she said, overly solicitous.

Steve laughed at him and scampered towards the edge of the sill, about to jump off, but Bucky yelled, "Wait!"

"What? What's wrong?"

"Let me." Bucky turned his head to gesture at his back.

Steve stared at him, then sat back on his haunches, ears canted backwards in disapproval.

Bucky's ears curved forward. "I like it," he said softly.

After a moment, Steve's ears relaxed. "For a mighty predator, you can be awfully soft. Starting to think I was on the money with that gooey kitten comment after all."

"Shut up and get on, will you?" Bucky grumbled.

Steve did, settling between Bucky's shoulder blades, and Bucky leapt to the floor and sauntered after Natasha, following her to her workroom, Steve's tiny weight feeling heavy again. He couldn’t even begin to explain the impulse that had made him stop Steve from jumping. The distance to the floor was nothing, not for Steve. Bucky knew that. Just like he knew Steve hated being coddled. But something was off, something not quite right, something he couldn’t articulate but could  _feel_  and it had sent the words blurting out of his mouth.

He shelved it to think about later, because right now, Natasha needed him to do his job.

He jumped up onto the table and Steve hopped off his back, making himself comfortable at the edge, tail held between his paws, his rune shining slightly silver in the residual magic of the workroom. Bucky leapt from the table's edge to the stool in front of Natasha, who was holding a twisted silver amulet in her hands.

Bucky eyed it dubiously, because Natasha didn't usually work with metal.

"Clint made it," she explained.

Bucky eyed it with even greater dubiousness. Clint had a positive gift for ear scratches, but not everything went right when he was involved.

"It'll be fine," she said, reassurance and amusement warring for supremacy in her tone. "He had help. It's our birthday gift for Sam, for protection, to help keep him safe when he's working. We don't want it going wrong."

Bucky flicked his ears forward, nosing it curiously when Natasha held it out. Sam had a  _bird_  as a familiar, which demanded a certain amount of disdain, but Sam was always kind to Steve, treated him with respect, so if pushed, Bucky would admit he liked him.

But only if pushed. 

Magic began to rise, ruffling Bucky's fur, whistling around the room like a growing storm. Power flowed through him, the storm contained, controlled, and sparks danced between him and Steve, the power gaining strength and stability with each jump before Bucky sent it on to Natasha.

This was what he did. It was, he thought, what he'd been born to do. He'd been a kitten, he'd been a stray, he'd been a street cat and king of the alleys, but this, this was what he was meant for, standing between Natasha and the full wild force of the magic, Steve helping him steady and balance it.

In these moments nothing was hidden between familiar and witch, but he'd never cared. He had nothing to be ashamed of. He had nothing to hide. That was a human thing. He was a cat and cats were always themselves, just as hard as they could be. If someone didn't like it, they could chuck themselves in the closest body of water.

Which meant Natasha could feel his utter joy at Steve's fire, at his golden, pure presence, at the flavour he gave the magic; she could feel how much he loved it, how much he loved Steve, and he knew how pleased she was for him.

It wasn't until they were done, until he'd let the power go and curled up around Steve, drifting off to sleep smelling of cloves and pine, that he realised Steve's fire hadn't burned quite as bright as it used to. 

Two nights later, Natasha left the apartment with a scratch behind Bucky's ears, a stroke down his back, and an exchange of gentle touches with Steve. "Don't wait up," she said as she headed out the door. "I won't be back tonight."

Bucky's enquiring  _mrrow_ prompted her to say, "Sam's birthday party. Don't worry," she added mischievously as she pulled the apartment door shut, "I won't tell him  _or_  Redwing that you helped with his present." 

"I swear," Bucky said when he was standing naked and human, "she could practically be a cat."

Steve, just as naked, just as human, grinned at him.

With Natasha gone, neither of them bothered with clothes, since Steve shared Bucky's eminently sensible opinion on the human obsession with them. Instead, they snuggled under a thick blanket on their couch, Steve curled against Bucky's left side, head resting on his shoulder as he brushed one hand over Bucky's skin in a constant wave of slow, gentle motion. The other was wrapped around a gigantic mug of hot chocolate, holding it balanced on his blanket-covered knee. 

They only had one mug between them, because it was easier to share. That way Bucky didn't have to worry about wasting his hand hanging onto a mug when he could be using it to touch Steve. Which was what he was doing, running his fingers through Steve's hair, wrapping them around his chin and gently pulling his head around to kiss him.

With a happy sigh, he pressed his cheek against Steve's hair and closed his eyes. Cats were obviously superior (not to mice, or at least not to one _particular_ mouse) but humans had some definite advantages.

The mug pressed against his lips, and he took a sip as Steve tilted the mug, opening his eyes to find Steve smiling at him.

"Spoiled."

He didn't deny it, just gave Steve a chocolate flavoured kiss.

"You're as bad as a human," Steve told him, "celebrating just because they get older."

"Hmmmm?" He was too busy alternating between pressing kisses along Steve's cheek and rubbing his cheek against it to pay much attention.

"Humans. Having a party just because they lived another year."

"Can you blame them? Lots of free parties," he yawned and tugged Steve closer, "and even better, lots of free presents. I wouldn’t say no to lots of free presents."

"How many are we talking here?"

"Parties or presents?" Bucky asked, grinning when Steve laughed, and he ran his nose up the side of Steve's neck, nuzzling into his hair.

"Both."

"I dunno, a bunch of each. Sam's twenty-seven, I think Natasha said. Imagine all the presents he must have racked up over the years."

Steve made a surprised sound and took a sip of hot chocolate, then held it so Bucky could take one; he didn't, just stared curiously at Steve. "What was that noise for?"

"That's  _old_."

"Is it?"

"I think so. Isn't it?"

"How old are you?" Bucky asked.

"I don't know. How old are you?"

"Nine, I think. Close enough, anyway."

Steve blinked at him. "Nine _._ "

" _Maybe_  ten, but I think it's nine. You really don't know how old you are?"

"I guess I can work it out. How long have I been with you?"

"It's been about ten months since I took you out of the cage." Ten months of Steve, ten months of his mouse, ten months of the best part of his life. Bucky snuggled Steve closer and Steve turned into him with a small, contented sound, throwing a leg over Bucky's thighs and shoving the mug onto the table so he could wrap both arms around him.

"I think," Steve said, voice a little muffled because his face was pressed into Bucky's shoulder, "I was in it for a bit less than that. Before that was the big tank with the other mice, where they were going to feed me to the snake."

The old anger roared back, the idea of Steve being  _food_ , Steve being  _prey,_ all wrapped around with the memory of Steve trapped in the tiny cage, staring out at him dull-eyed, no food, no water. He squeezed him tighter. "No more cages, Steve. Not ever."

"I know."  

"You could have died."

"I would have died," Steve corrected. "But you came for me." He leaned back and met Bucky's eyes. Steve's eyes were blue, not bright, gleaming black, but they were still his eyes. Still held the same clever stubbornness. It was still Steve looking out at him. "You got me out."

It was too much. Words were useless. Bucky pressed up to kiss Steve, met Steve leaning forward to kiss  _him,_  and it was glorious, it was perfect. Steve shifted them, pressed him down to the couch, the blanket tangled around them as Steve went to work with hands just as clever as his paws, drawing gasps and moans and sighs out of Bucky. Bucky flattened his hand against Steve's back, palm covering the rune inscribed over Steve's spine, and his last coherent thought before his brain gave up entirely was thanks for the gift Natasha had given them.

The next morning, they were both still human when the sun rose. Steve was sleeping, curled into Bucky's side, one hand clutching Bucky's arm. Bucky's arm was wrapped around him, holding him close, his cheek against Steve's hair, and his thoughts had entirely returned to coherence.

Steve was a little over a year and a half old, give or take. Bucky remembered what he'd been like at that age, and it was nothing like Steve. He'd barely been full grown, and he only really remembered because it was right around then that the family who'd brought him home as a tiny, bumbling kitten—who'd loved him when he'd been a tiny bumbling kitten—had stopped letting him in the house altogether.

However small Steve was, however short a life he'd lived, he  _wasn't_  barely grown.

Cats didn't need to wonder how long mice lived, because they _knew_ : mice lived exactly as long as it took a cat to pounce and  _bite_.

But Bucky wasn't just a cat. He was Steve's cat. Steve was his mouse. And Steve had started sleeping through sunsets, started slowing down on his wheel. Steve's fire hadn't burnt as bright.

He needed to talk to Natasha.

Bucky waited through the day, and he waited through sunset, and he waited until Steve was sleeping and then he changed, calling on the power of the rune tattooed on his back. Natasha had given it to him—with his permission, with his consent—so that he could make his own choices, but truth was, he didn't need it anymore. He knew how to work the spell himself, just like he knew how to work so many of her spells, because she'd always been generous with him, teaching him whatever he wanted to learn.

She trusted him, just like he trusted her, and so he changed into a human and went to ask her about Steve.

He was halfway down the hall to her bedroom when he remembered about clothes, had to turn around and pull on the sweater and pants she insisted he wear before heading back, but he could hear she was awake so he tapped on the door.

"Come in."

He pushed the door open and she smiled up at him, setting her book aside.

He shifted from foot to foot. "I need to talk to you."

She waited patiently.

"About Steve."

"Is something wrong?"

"Maybe. I don't know. How long do mice live?"

Bucky currently looked human but he was, and always would be, a cat, and he knew Natasha very well. Something moved behind her eyes, something dark, something sad, and he didn't think. He  _pounced_ , crossing the room in a single leap, ending crouched next to her bed, but she didn't flinch.

" _Tell me_."

"Not very long."

Bucky curled his fingers into the quilt; if he'd had claws, he would have shredded it. "He's slowing down."

She nodded.

"Because he's getting old."

She nodded again.

"How long?"

"A billion heartbeats."

Bucky stared at her.

"It's how long you get. It's how long you all get. A billion heartbeats, Bucky. Compared to humans cats don't live long—not you; you're my familiar, your heart's linked to mine, and the billion heartbeats doesn’t apply to humans—but compared to a mouse? A mouse gets a couple of years, Bucky. Maybe a little longer if they're lucky. A cat's heart beats much slower, your billion beats take longer, so next to them it's a very long life."

"Steve's going to die because his heart beats too fast?"

There was a sheen in Natasha's eyes, and she didn't answer, just gazed back at him.   

"That's not fair." Bucky pressed his forehead hard against her thigh and she pushed his hair behind his ears, rubbing gently. "It's not  _fair._ "

"I know."

Silence fell over them. Bucky had never cared about death before. It was something that happened. You fought like hell to beat it, but if you couldn’t, you couldn’t, and there was no point worrying about it. But knowing how close Steve had come to dying in the cage had rocked that indifference, like a vase at the edge of a shelf, and this…this sent it plummeting down to shatter on the tiles.

Natasha's hand was warm on his head, gentle and comforting, but he didn't want to be comforted. He wanted to fight. He wanted something he could sink his teeth and claws into. Something he could tear apart. Something he could  _beat._

"I've seen old humans. If Steve's getting old how come he doesn't look like them when he's human?"

"Because his human shape was made by magic, made for him, made  _of_  him." She went quiet, then added, "You cast the spell. His shape is partly formed by the way you see him." Bucky huffed quietly, because that explained a lot. "Aging would mean making a new shape and a new shape and a new shape, every time. That's not how it works. There's just the one, the one you created when you cast the spell, that we anchored to the rune on his back."

Hope bumbled into the room like a litter of clumsy kittens. "What if he stayed human?" He lifted his head to stare at Natasha's face. "Would that work? Could that work?"

He could see she was frustrated, feel it in the way her hand tightened in his hair, and he didn't understand why, but he didn't care. This could be an answer. This could save Steve.

"If he stayed human, yes. He wouldn't age. When you're human, your bodies are on hold. But Bucky—"

He didn't let her finish, just surged to his feet and pelted out of the room back to Steve.

Steve was sleeping curled at the edge of Bucky's bed and Bucky carefully scooped him up in his hand. He shocked awake, startled, body tense, alert, tail flicking, but Bucky brought him to his face, touched his nose to Steve's, and said, "I need you to change." 

He set him down on the floor and stepped back, waiting impatiently. If he'd had a tail, it would have been lashing. He had to fight down the urge to twitch his butt back and forth.

In moments, Steve was standing naked and human in front of him, arms folded. "That's a shitty way to wake me up, Bucky. You're lucky I didn't bite you."

"Sorry, sorry." He ran his hand over Steve's shoulder, down his arm to his hand, and caught it, drawing him forward.

Steve tipped his forehead against Bucky's shoulder with a quiet sigh and brought his hands up to press them against Bucky's chest. "Seriously, I should have bitten your  _nose_." But he didn't sound mad and he was stroking his hands over the front of Bucky's sweater.

Bucky gathered him close and rubbed his cheek over Steve's hair. "Sorry, but I need to talk to you and it can't wait."

"This better be good." Steve yawned and flopped against Bucky, tilting his head to kiss his chin, rubbing his cheek against the scratchy stubble. "I was sleeping."

"I know. Steve." He took a deep breath and stopped. His courage deserted him. What did he  _say._

"Bucky?" Steve peered up at him. "If you woke me up to say my name I'm gonna be irritated."

"No, no, I know." Bucky got a hold of himself. He was a  _cat_ , but maybe what he really needed to be right now was a mouse. Bravest of the brave, boldest of the bold. Right. "Steve, mice don't live very long."

Steve blinked up at him.

"You're old."

"What are you getting at?"

"I'm getting at you're old. You're going to die."

"We're all going to die."

"Not  _soon_."

Steve stared at him unblinking, fingers curled in Bucky's sweater. "You're trying to save me again?"

" _Yes_. And it's easy. All you have to do is stay like this."

Steve looked down at himself. "Like this."

"If you stay human, you won't age. It's perfect." He wanted to purr, he wanted to strut. He wanted to groom his whiskers in satisfaction, because it was so simple. So easy. So—

"No."

"No?"

"I'm a mouse. I'm not a human. I don't want to be a human."

"Not even to save your life?"

"No."

The car that hit Bucky had come out of nowhere. It had come out of nowhere and torn the world apart.

It was happening again.

Steve's eyes were bright in the darkness.

"Not even for me?" It was quiet, so quiet. Steve's eyes closed.

"Not even for you. I'm sorry. I love you, but I can't live as something I'm not. Not forever, not like you're asking."

Steve wrapped his arms around Bucky and held on with all his wiry strength and Bucky buried his face in Steve's hair. There was a lump in his throat, his eyes were burning, and he didn't know what was wrong with him. There was something wrong with this stupid human body. He clung to Steve.  

"But we can stay human more. We can stay human a lot. Just not forever. Just not all the time."

His cheek was pressed against Bucky's and Bucky knew he was trying to comfort him, but Bucky still didn't want comfort. He wanted this to  _stop_. He wanted the pain to stop. He wanted his heart to stop hurting, aching, feeling like it was being torn from his body like his leg had been.

It wasn't  _fair_. A billion heart beats wasn't enough. He needed more, so he could give them to Steve and then it wouldn’t matter how fast his heart beat, he could—

Bucky stopped. Went still. Stared into space over Steve's head. Oh.  _Oh._ "I'm so stupid," he groaned, and grabbed Steve's hand, dragging him down the hall.

"Bucky. Bucky what are you doing. Bucky, I have to, what about, you can't—"  

But he could, and he was.

"Make him your familiar," he demanded as he threw open the door to Natasha's room.

"Clothes?" Natasha suggested mildly as Bucky vibrated in the doorway, clutching the hand of an entirely naked Steve.

Steve gently freed his hand from Bucky's. "I tried to tell him," he said to Natasha, then patted Bucky's shoulder. "Wait here."

He came back wearing pants and a shirt and slipped his hand back into Bucky's.

"Make him your familiar," Bucky said, more calmly this time. "That's what you were hinting at before, wasn't it?"

Natasha carefully didn't look at Steve. "I can't ask him to be my familiar."

"What? Why not? You asked me." He bristled. "What's wrong with him?"

"There's nothing wrong with him," she soothed. "But Bucky, magic has rules. You know that. And one of those rules is that a witch can ask for a familiar, but she can only ask once. And I asked you."

"That's stupid."

Natasha tilted her head in acknowledgement. "Maybe. But no one wants a witch to build herself a familiar army. That's…not good. So going around asking isn't allowed. But if one were to offer..." She trailed off, giving Bucky a pointed look. "That would be different. Familiars don't offer themselves to the kind of witches who'd create armies." The corner of her mouth twitched up. "Or that's the theory."

Bucky scowled. "Who'd know?"

"The magic knows. And the magic isn't something you want to cross."

That gave him pause, because she was right. But… He turned to Steve, who was watching him carefully.

"Natasha's yours. I can't take her from you."

"There's nothing I have I wouldn’t give you. There's nothing I am I wouldn't give you." He swallowed around that stupid lump in his throat. "Steve. Please."

Those clever hands came up to cup his face, to stroke his cheeks, to slide into his hair, and he leaned closer to press his cheek to Bucky's. "Yes," he whispered in his ear.

Fierce love roared through Bucky. He grabbed Steve around the waist and hoisted him up, Steve's legs leaving the ground as his arms clutched at Bucky. Bucky spun him around, carolling his joy, and Steve smacked him. "Put me down, you idiot."

Bucky let him slide down his body, wanting desperately to purr. He managed something like a rumble and nudged his nose against Steve's neck, nuzzling behind his ear. Steve held him close, then turned towards Natasha. Bucky looped his arm around Steve's waist and pulled him back against his body.

Natasha was wearing a look of mild curiosity, as if she had no idea what they were doing in her room, or what they could possibly be so happy about.

"Natasha."

"Yes, Steve?"

"I'd like to be your familiar. As well as Bucky, not instead of," he added. "If you'll have me."

The smile she gave them was so bright it almost lit up the room and Bucky felt the faintest tug of magic, felt it ruffle through his hair, felt it  _listening._

"I'd welcome you, Steve. In turn I offer my protection for as long as you live, even if you choose to stop being my familiar."

It felt like a key turning in a lock.

"We can do the binding ceremony tomorrow. After we get some sleep," she said. "Steve, can you give us a moment?"

Steve nodded, leaned up to press his forehead against Bucky's cheek, then left.

When he was gone, she said, "You need to know, if you hadn't come to me, hadn't asked about Steve, about him getting older, hadn't figured out the familiar option, I was going to come to you. Screw the consequences. I wouldn't have let you lose him."

Words weren't enough. Bucky sat on the edge of her bed and rested his forehead against her shoulder, smiling when she ran her fingers over his hair. 

After a few minutes, she said, "Steve'll be wondering where you are."  

Bucky left, but paused as he was about to pull the door shut behind him. "I've never regretted, I will never regret, becoming your familiar."

"And I'll never regret asking you." She made a shooing gesture. "Go find your mouse."

Natasha knew all kinds of complex magic, complicated workings that could alter the structure of the world. Binding a familiar wasn't one of them. At its heart, it was simple, about will and willingness and promise as much as it was about magic.

The next morning, Steve held very still while she delicately drew a pattern of silver and blue in pale light on his fur. When she was done, he caught her finger between his paws, holding tight, and pressed his nose against her skin.

Bucky sat next to him on the workroom table, his tail curled to make a circle around Steve's body.

This was simple, but even simple things had to be done carefully. Simple, but it would create a near-unbreakable bond. Simple, but it would take power.

What so many people got wrong about magic was that they thought it was a hammer, something that would do exactly as they wanted. But magic wasn't a dumb tool to be wielded. It was more like a river. Not quite alive, but sometimes, no matter the dams you built or the diversions you dug, it went where it pleased and woe betide the humans—or cats or mice—who thought they could tell it differently.

Natasha called and the magic answered, power flowing through Bucky, ruffling his fur, sparking between him and Steve, only this time Steve wasn't on the periphery. This time, he was right in the middle, his gorgeous, glowing golden true-self the focus of the spell.

The binding was simple, to tie Natasha's heart to Steve's, but Bucky could feel it twisting away from her, feel it sliding and slipping and he pounced on the power, holding it between his metaphorical paws like particularly troublesome prey as it writhed and twisted. Natasha's spell met it head on, the two tangling together like wild vines, blossoming into a vibrant waterfall of life that exploded into light, Bucky's golden self reaching for Steve's.

When the sparks faded, Natasha blinking her eyes to clear them, she took one look at them and started laughing.

The spell had worked. It had forged a humming bond, linking heart to heart, but the magic had made a different choice: it had bound Steve to Bucky.

Bucky stared at Steve, and Steve stared at Bucky. Bucky's ears curved sideways as Steve groomed his whiskers, then Steve tilted his head and bounded over to press his front paws against Bucky's chin.

"He's your familiar," Natasha finally managed to get out around her laughter, and Steve's head whipped around in her direction. "A familiar with a familiar."

Bucky stared at her, hunching himself protectively over Steve, because that wasn't what was supposed to happen.  _How did that help?_

She was his witch; he'd always be an open book to her. Her voice was gentle as she said, "Bucky. You're bound to me, Steve's bound to you. He'll live as long as you, you'll live as long as me. In the end it's the same."

Bucky stared down at Steve. He had the entirely un-cat like sensation of having no idea how to react. Steve snapped him out of it by tugging on his whiskers. "I'm your familiar?"

"I guess you are."

"What does that mean?"

"It means," how had Natasha put it? "your heart's linked to mine."

Steve hummed, low and long, and bumped his nose against Bucky's. "It already was. What does it mean in  _practical_  terms?"

A purr rumbled out of him, filling the air around them, loud and strong and so damn happy. He rasped his tongue across Steve's back and lay down so he could curl his front leg around Steve.  _It already was._ His mouse. His perfect, glorious mouse. "It means we'll have a long time together to figure it out." 

**Author's Note:**

> Thank you for reading, and a very happy birthday to Steve Rogers! 
> 
> In case anyone's wondering: 1 mouse month = 7.2 cat months/32 human months; 1 cat year = 4.5 human years, assuming life spans of mouse: 30 months, cat: 18 years, human: 80 years. Steve, however, would have had a quite reduced life expectancy due to his poor start in life and poor living conditions (and 30 months is very generous for a mouse, supposing ideal conditions and good breeding) before Bucky and Nat got him (and he probably wasn't the best bred mouse to start with, which would have dropped it even further).


End file.
